OPA
268
4
OPA2684
SBOS239B – APRIL 2002 – REVISED NOVEMBER 2002
Low-Power, Dual Current-Feedback
OPERATIONAL AMPLIFIER
FEATURES
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MINIMAL BANDWIDTH CHANGE VERSUS GAIN
170MHz BANDWIDTH AT G = +2
> 120MHz BANDWIDTH TO GAIN > +10
LOW DISTORTION: < –82dBc at 5MHz
HIGH OUTPUT CURRENT: 120mA
SINGLE +5V TO +12V SUPPLY OPERATION
DUAL
±
2.5 TO
±
6.0V SUPPLY OPERATION
LOW SUPPLY CURRENT: 3.4mA Total
APPLICATIONS
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SHORT-LOOP ADSL CO DRIVER
LOW-POWER BROADCAST VIDEO DRIVERS
DIFFERENTIAL EQUALIZING FILTERS
DIFFERENTIAL SAW FILTER POST AMPLIFIER
MULTICHANNEL SUMMING AMPLIFIERS
PROFESSIONAL CAMERAS
ADC INPUT DRIVERS
DESCRIPTION
The OPA2684 provides a new level of performance in low-
power, wideband, current-feedback (CFB) amplifiers. This
CFB
PLUS
amplifier is among the first to use an internally
closed-loop input buffer stage that enhances performance
significantly over earlier low-power CFB amplifiers. While
retaining the benefits of very low power operation, this new
architecture provides many of the benefits of a more ideal
CFB amplifier. The closed-loop input stage buffer gives a
very low and linearized impedance path at the inverting input
to sense the feedback error current. This improved inverting
input impedance retains exceptional bandwidth to much
higher gains and improves harmonic distortion over earlier
solutions limited by inverting input linearity. Beyond simple
high-gain applications, the OPA2684 CFB
PLUS
amplifier per-
mits the gain setting element to be set with considerable
freedom from amplifier bandwidth interaction. This allows
frequency response peaking elements to be added, multiple
input inverting summing circuits to have greater bandwidth,
and low-power line drivers to meet the demanding require-
ments of studio cameras and broadcast video.
The output capability of the OPA2684 also sets a new mark
in performance for low-power, current-feedback amplifiers.
Delivering a full
±4Vp-p
swing on
±5V
supplies, the OPA2684
also has the output current to support >
±3Vp-p
into 50Ω
loads. This minimal output headroom requirement is comple-
mented by a similar 1.2V input stage headroom giving
exceptional capability for single +5V operation.
The OPA2684’s low 3.4mA supply current is precisely trimmed
at +25°C. This trim, along with low shift over temperature and
supply voltage, gives a very robust design over a wide range
of operating conditions.
V+
1 of 2 Channels
BW (MHz) vs GAIN
6
Normalized Gain (3dB/div)
3
0
–3
–6
–9
–12
–15
–18
–21
–24
10
R
F
= 800Ω
MHz
G = 10
G = 20
G = 50
G = 100
G=5
G=1
G=2
+
V
O
V–
I
ERR
R
F
Z
(S)
I
ERR
R
G
Low-Power
Patent Pending
Amplifier
100
200
Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of Texas Instruments
standard warranty. Production processing does not necessarily include
testing of all parameters.
Copyright © 2002, Texas Instruments Incorporated
www.ti.com
ETC [ ETC ]
